As a conventional waveform generation circuit, JP 2004289597A (US 2004/0141560 A1) discloses one exemplary circuit, which includes a switching element, a monitor circuit, an output current control circuit and the like. The monitor circuit is configured to monitor an output current flowing in the switching element when the switching element is turned on. The output current control circuit is configured to switch in steps a slope (change rate) of the output current based on the monitor result of the monitor circuit, so that the output current of the switching element changes in the form of the sinusoidal wave.
According to the conventional exemplary waveform generation circuit, the slope of the output current is switched over in steps. As a result, the waveform of the sinusoidal wave results in a combination of a plurality of straight lines. At each part (angle), where the slope of the output current changes, noises are generated.